1. Field of the Invention
This invention relates to bowling pins having a foam plastic core and a solid plastic shell molded thereon and secured thereto by a greatly increased interface area.
2. Description of Related Art
Short supply of suitable woods make important the development of plastic bowling pins, whose performance in competition must be equivalent to approved wood pins.
Experimental bowling pins have heretofore been made with plastic shells molded over wood or foam plastic cores. Such pins have experienced serious problems of separation of the shell from the core. There have been some attempts, as in U.S. Pat. No. 3,971,837 to Hasegawa, to solve this problem by forming a few grooves in the exterior surface of the core, and casting the plastic shell thereabout. The grooves so formed do not appear to afford any substantial increase in area of the shell-to-core interface.
British Patent No. 1,058,307 discloses a proposed bowling pin having an expanded monomer foam core about which is molded a similar monomer shell; it discloses that pouring the liquid monomer shell plastic around a pre-formed monomer core softens and partially solvates the core so as to form a chemical union between the previously formed monomer core and the monomer shell. Neither monomers nor thermoplastic polymers would ordinarily be considered as suited for bowling pin cores, since they would soften under the heat of the later-mold shell. FIG. 7 of the British patent shows the outer portions of the core have been so badly distorted by such softening, when the shell was poured about it, as to lose concentricity. Applicant doubts whether such pins have even been put to use, because resultant variations must affect the dynamic characteristics of the pin.